Cavity resonator magnetron



June 10, 1947.

S. T. MARTIN, JR CAVITY RESONATOR MAGNETRON 2 Sheets- Sheet 1' Filed NOV. 14, 1942 INVENTOR, fry/7r Z finer/17h.

June 10, 1947. s, I JR I I 2,422,028

CAVITY RESONATOR MAGNETRON Filed Nov. 14, 1942 z sneets-sheet 2 INVENTOR Patented June 10, 1947 UNITED CAVITY RrsoNA'roR MA NE RON 1 Stuart "IL-Martin, Jr., Arlington, va, assignor to RadioCorpor'ation of America;

tion of Delaware a corpora- .Application'November 14, 1942, sens tive. 465,5 4

1 My invention relates to electron discharge devices useful at ultra, high frequencies, more par-- ticularly to magnetrons utilizing resonant cavity circuits. 1

In one form of magnetron utilizing resonant cavity circuits or resonators, an elongated cath- Ode is surrounded by an anode member comprising a large mass or cylindrical block of conducting material having a central cylindrically shaped cavity coaxial with said cathode. Radially directed slots extend from the surface ofthe cylindrical cavity to provide a plurality of anode segments the surfaces of whichdefine the cylindrically shaped cavity. The outer ends of the slots communicate with cylindrically shaped cavities within the anode block. These last mentioned cavities are parallel to the cathode and coextensive therewith and symmetrically positioned about the central cavity. There is thus provided aplurality of resonatorsor resonant cavity circuits surrounding the cavity and connecting adjacent anode segments. The ends ofthe anode block ore provided with cup-shaped depressions and are closed by conducting discs or plates with a vacuumtight seal. permanent magnet is positioned to provide a magnetic field parallel to the cathode and between the cathode and the anode segments.

In a device of this kind, referred to as a multiresonant cavity magnetron, different modes of oscillation may exist at the same time. It is usually the case that a magnetron of the cavity type will operate simultaneously in more than one mode. Since the different modes have frequencies differing by an amount greater than the band pass of the receiver used in conjunction with the transmitter energized by the magnetron, the undesirable modes represent an effective loss of power and efficiency.

It has been found that the most eflicientmode of oscillation is one in which the flux in alternate cavities goes in opposite directions, that is adjacent resonant cavities operate in push-pull or 180 out of phase. Less efiicient modes in general operate with different phase relations than this between adjacent cavities.

Attempts have been made in the past to eliminate undesirable modes by electrically tying the anode segments together in different ways and while some improvement may result the frequency of the mode is decreased in a not readily predicted way due to the effective increase in capacity of the resonators due to the electrical connections between anode segments.

It is, therefore, an object of my invention to provide an electron discharge device of the magnetron type of improved design and utilizing resonant cavity circuits or resonators.

Another object of my invention is to provide such a device in which undesirable modes of s- An electromagnetic coil or 10 Qlaims. (Cl. 250-275) cillation in a mulitiple resonant cavity type of magnetron are suppressed or substantially eliminated. A further object of my inventionis to provide a magnetron of the resonant cavity type in which suppression of the undesirable modes of oscillation is accomplished without reducing the frequency. of the desired mode of oscillation appreciably. Furthermore, the suppression is achieved in such a waythat the efiectsof suppressing devices are not difficult to calculate. A still further objectof my invention is to provide a magnetron utilizing resonant cavities in which the suppression of undesirable modes of operation is accomplished by means of simple electrical structures which do not requireredesign of theelectr'odes or the resonator structures. The novel features which I believe to be characteristic of my invention are'set forth withparticularity in the appended claims, butthe invention itself will best be understood by reference to the following description taken in connection with the accompanying "drawing in which Figure l is a plan view with'jcovler removed of an electron discharge device made according to my invention, Figure 2jis a vertical longitudinal section with the coverin' place of an electron discharge device shown in Figural, Figure 3 is an elevation partially in section of a modification of an enema discharge device made according to my invention, Figuresfl and 5 are partial perspectives showing the relationship of the loops and the resonant cavities of the devices shown mi i ure'sna ds,

'In Figures 1 and 2 is shown one form of an electron discharge device of the magnetron type using resonant (realities and made in accordance with'my invention. An-elongated cathode lllof the indirectly heated type is surrounded bythe cylindrical anode block ll of conducting material, preferably copper. This anode block is provided with a central cylindrically shaped chamher [2 extending therethrough'and coaxialwith the cathode 10. This chamber may be referred to as the anode space. A plurality of cylindrically'shaped cavities l3 extend lengthwise of the block and parallel to the central cylindrical chamber l2. Radiall y directed slots, [4 connect the; central chamber [2 with the cavities l3. Thus there are provided a plurality of anode segments [5 between adjacent slots.

In effect each anode segment is connected to thetnext' adjacent anode segment by a resonant cavity circuit having inductance andcapacity and the'natural frequency of which is determined by the diameter of, the cavity and the dimensions of theslot connecting it to the central anode space, The smaller the cavity the higher the frequency at which the device will function. V Asbst shown inFigure 2 the anode block is provided at each end with a cup shaped depression l6 and I! and the ends are closed by the disc shaped cover members I8- and H! which may be brazed or soldered to the anode block with a vacuumtight seal.

The cathode is supported within the anode block by means of the leads and Support wires l" electrically connected to the collar I 0" secured at each end of the cathode. The electron shields 20 and 2| are also supported from these leads and are positioned between the ends of the cathode and the disc closure members and la.

The support wires I0" form the inner conductors of coaxial cables, the outer tubular members 22 and 23 of which are sealed by means of the cup-shaped seals 24 and 25. If desired, coaxial line tuning member can be secured to the members I8" and 22 and 23 for tuning the-cathode leads to prevent R.-F. currents from being directed into these leads.

To extract energy from th magnetron a coupling loop 26is positioned within one-of the cavities, a lead 26' being connected to the loop and forming the internal conductor of a coaxial line cable, the outer conductor 21 of whichis provided with a threaded portion which can be secured to the outer conductor of the coaxial line cable which may be attached to conductors 26 and 21. The elongated cup shaped member 28 seals 01f conductors 26 and 21.

Radiating fins 29 may be secured to the anode block to cool the block during operation of the magnetron. A permanent magnet. 30- ofv U-shape may be utilized to provide the magnetic field extending longitudinally of the cathode and the anode block.

In accordance with my invention I provide closed loops of conducting material, such as copper, which are positioned just above and diagonally across the cavities in a radial direction and lying in a radially positioned plane passing through the cathode, such that when the tube is operated in the proper mode no flux will pass through these loops. Any tendency of the tube to oscillate in a less eflicient mode will of necessity cause magnetic flux to link these loops. Being of conducting material currents will be induced within the loop which will tend. to prevent a magnetic flux from passing through the loop and thus any undesired mode will be suppressed. The effect of the loop may be thought of as decreasing the mutual inductance between the cavities when they are oscillating in a low efficiency mode but not afiecting the mutual inductance when they are operating. in the proper mode.

In one form of the invention the conducting loops 31 are secured to the top and bottom closure members I8 and I9 and are suspended in the proper position relative to the cavities. An enlarged view in perspective of the relationship of the loop with respect to the cavity and cover is shown in Figure ]..v The loop lies in a plane passing radially and. longitudinally through the cathode. The essential requirement with respect to the plane in whichv the loop lies is that the plane be one of symmetry with respect to-the cavity, regardless of the form of the cavity o the position of the cathode, in order to suppress magnetic flux linkages between resonant cavities over any paths except those paths the flux would naturally take when the device oscillated in the desired mode.

In Figure 3 is shown a modification of the device shown in Figures 1 and 2. Like numbers form is shown in Figure 5.

With the arrangement disclosed the undesired modes of operation are suppressed with little or no shift in frequency. It has been experimentally observed that when the cavities resonate in the undesirable mode a loop placed in the position shown will pick up appreciable voltage, indicating flux across the top of the cavity. When resonating in the push-pull modes no voltage is picked up by the loop. As a result the proper mode of operation is encouraged while undesired modes of operation are suppressed. With my arrangement no structural changes are necessary either in the electrode structur or in the structure of the cavities utilized with my invention. It is of course obvious that the shapes of the cavities utilized in m invention are not critical and that other cavities having a different transverse section could be utilized.

While I have indicated the preferred embodiments of my invention of which I am noW aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device having a cathode for supplying electrons, a plurality of anode segments surrounding a space into which the electrons from said cathode are directed, conducting means connecting said segments and providing cavity resonators between said segments, and a conducting loop positioned adjacent one end of the conducting means but outside said conducting means and lying in a plane passin longitudinally through one of said cavity resonators and symmetrically with respect thereto.

2. An electron discharge device having an elongated cathode, a plurality of anode segments surrounding and parallel to said cathode, conducting means connecting said segments and providing cavity resonators between said segments, anda conducting loop positioned adjacent one end of the conducting means but outside said conducting means and lying in a plane passing longitudinally and symmetrically through one of said cavity resonators.

3. An electron discharge device including a cylindrical conducting member having a central chamber extending longitudinally of said cylindrical conducting member, aid conducting member having a plurality of cavities positioned symmetrically about and parallel to said chamber and having slots connecting said chamber and said cavities providing a plurality of anode segments connected by cavity resonators, a cathode positioned within the confines of said electron discharge device to supply electrons within said chamber, means for providing a magnetic field parallel to the longitudinal axis of said cylindrical conducting member within said chamber and a conducting loop supported at one end of said cylindrical conducting member and lying in a plane passing longitudinally and symmetrically through one of said cavities.

4. An electron discharge device having an elongated cathode, a plurality of anode segments surrounding and parallel to said cathode, conducting means connecting said segments and providing cavity resonators between said segments and a conducting loop positioned adjacent one end of the conducting means and lying in a plane radially bisecting one of said cavity resonators.

5. An electron discharge device including a cylindrical conducting member having a central ,opening extending longitudinally of said cylindrical conducting member, said conducting member having a plurality of cavities positioned symmetrically about and parallel to said central opening and having radial slots connecting said central opening and said cavities and providing a plurality of anode segments, a cathode positioned within said central opening, means adjacent said device for providing a magnetic field parallel to the longitudinal axis of said cylindrical conducting member and said cathode and a conducting loop supported at the end of said cylindrical conducting member and lying in a plane passing longitudinally and symmetrically through one of said cavities.

6. An electron discharge device including a cylindrical conducting member having a central cylindrically shaped cavity extending therethrough longitudinally of said cylindrical con ducting member, said cylindrical conducting member having a plurality of cylindrically shaped cavities positioned symmetrically about and parallel to said central cavity, and having radial slots connecting said central cavity and said cylindrical cavities and providing a plurality of anode segments therebetween, a cathode positioned axially of said central cavity, means adjacent said device for providing a magnetic field parallel to the longitudinal axis of said cathode, and con. ducting loops supported adjacent the ends of each of said cavities, and each loop lying in a plane passing radially and longitudinally through said cathode.

7. An electron discharge device including a cylindrical conducting member having a central opening extending longitudinally of said cylindrical conducting member, said conducting member having a plurality of cylindrically shaped cavities positioned symmetrically about and parallel to said central opening and having radial slots connecting said central opening with said cylindrical cavities and pro'viding a plurality of anode segments, a cathode positioned within said central opening, means adjacent said device for providing a magnetic field parallel to th longitudinal axis of said cylindrical conducting member, a closure member at the end of said cylindrical conducting member, said cylindrical conducting member being provided with a space between said closure member and the ends of said cylindrical cavities, a plurality of conducting loops within said space, said conducting loops being positioned adjacent the ends of said cylindrical cavities, and lying in planes radially bisecting said cylindrical cavities.

8. An electron discharge device including a cylindrical conducting member, one end of which is recessed providing a cup-shaped depression, and having a central opening extending -longitudinally of said cylindrical conducting member,

said conducting member having a plurality of cylindrical cavities positioned symmetrically around and parallel to said central opening and having radial slots connecting said central opening and said cylindrical cavities together and providing a plurality of anode segments, a cathode positioned axially of said central opening, means adjacent said device for providing a magnetic field parallel to the longitudinal axis of said cylindrical conducting member, and a closure member at the end of said cylindrical conducting member for closing the end or the cylindrical conducting member provided with said cupshaped depression and a plurality of loops supported from said closure member and positioned adjacent the ends of said cylindrical cavities, and radially bisecting said cylindrical cavities.

9. An electron discharge device including a cylindrical conducting member, one end of which is recessed providing a cup shaped depression, and having a central opening extending longitudinally of said cylindrical conducting member, said conducting member having a plurality of cylindrical cavities positioned symmetrically around and parallel to said central opening and having radial slots connecting said central opening and said cylindrical cavities together and providing a plurality of anode segments, a cathode positioned axially of said central opening, means adjacent said device for providing a magnetic field parallel to the longitudinal axis of said cylindrical conducting member, and a closure member at the end of said cylindrical conducting member for closing the end of the member provided with said cup-shaped depression, and conducting loops extending from the sides of said cup-shaped depression and lying in planes radially bisecting said cylindrical cavities.-

10. An electron discharge device including a cylindrical conducting member, each end of which is recessed providing a cup-shaped depression and having a central opening extending longitudinally of said cylindrical conducting member, said cylindrical conducting member having a plurality of cylindrical shaped cavities positioned symmetrically around and parallel to said central opening, and having radial slots connecting said central opening and said cylindrical cavities together, and providing a plurality of anode segments therebetween, a cathode positioned axially of said central opening, means adjacent said device for providing a magnetic field parallel to the longitudinal axis of said cathode and a closure member at each end of said cylindrical conducting member, and a plurality of conducting loops supported from said closure members and positioned adjacent the ends of said cylindrical cavities within said cup-shaped depression and lying in planes radially bisecting said cylindrical cavities and passing through said cathode.

STUART T. MARTIN, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,209,923 Kilgore July 30, 1940 2,063,342 Samuel Dec. 8, 1936' 2,270,777 Von Baeyer Jan. 20, 1942 2,280,824 Hansen et al Apr. 28, 1942 

